PROJECT SUMMARY/ABSTRACT Sex differences in the propensity to develop substance use disorders (SUD) are well established, but research to determine the mechanistic underpinnings remains sparse. In recent years, the number of women with SUD has markedly increased and the number of adolescent girls using stimulants has exceeded that of boys. Given that females are more sensitive to drugs of abuse, develop SUD more quickly, find it more difficult to quit once addicted, suffer greater withdrawal symptoms and exhibit shorter times of abstinence before relapse, this demographic shift in drug taking behaviors represents a public health crisis. Addiction is a medical, social and economic burden with few treatment options and none that are sex-specific. Therefore, it is imperative to understand the pathophysiology of addiction and how best to manage it, in men and women. In my career, I will build an independent research program that investigates and clarifies the cellular, molecular and circuit specific mechanisms of sex differences in drug addiction. This proposal will investigate the role of the medial amygdala (meAMY), a known sexually dimorphic region, in modulating sex differences in cocaine self-administration (SA). This Pathway to Independence Award will provide the opportunity to build on my expertise in sexual differentiation of the brain and cellular/molecular neuroscience while simultaneously developing my training in behavioral pharmacology and in vivo imaging and manipulation of circuit activity. In the mentored (K99) portion of this award, I will focus on characterizing sex differences in meAMY activity and its modulation of reward through sex-specific inputs to the ventral tegmental area (VTA). Under the mentorship of Drs. Eric Nestler and Veronica Alvarez, I will investigate how meAMY cellular activity is temporally associated with sexually dimorphic SA behaviors using fiber photometry to measure in vivo Ca2+ flux. This cutting-edge and powerful technique can probe meAMY cellular activity in a real-time during acquisition of cocaine SA, a sexually dimorphic behavior. With additional mentorship from Dr. Paul Kenny, I will study the functionality of sex differences in connectivity of the meAMY to VTA by chemogenetically inhibiting sex-specific meAMY ? VTA projections in males to reverse/reduce sex difference in SA acquisition. These experiments will prepare me to functionally interrogate the role of the meAMY as a mediator of sex differences in reward throughout mesolimbic dopamine pathways in the R00 portion of this award. My independent laboratory will investigate meAMY sex differences in modulation of glutamatergic inputs to the nucleus accumbens (NAc) during operant SA and characterize the role of these inputs in sexually dimorphic drug-seeking behaviors. In sum, the research proposed in this Pathway to Independence Award will reveal both separate and potentially interactive cellular and circuit-wide mechanisms underlying sex differences in addiction and drug abuse. More broadly, the added training afforded by this award will prepare me to launch an independent research program evaluating sex differences in reward, from molecules to circuitry, in a translational model of drug abuse.